U.S. patent application number 15/302845 was filed with the patent office on 2017-02-02 for method for preparing super absorbent polymer and super absorbent polymer prepared therefrom.
This patent application is currently assigned to LG Chem, Ltd.. The applicant listed for this patent is LG Chem, Ltd.. Invention is credited to Tae Bin Ahn, Chang Sun Han, Yong Hun Lee, Sung Jong Seo.
Application Number | 20170029576 15/302845 |
Document ID | / |
Family ID | 56193025 |
Filed Date | 2017-02-02 |
United States Patent
Application |
20170029576 |
Kind Code |
A1 |
Lee; Yong Hun ; et
al. |
February 2, 2017 |
METHOD FOR PREPARING SUPER ABSORBENT POLYMER AND SUPER ABSORBENT
POLYMER PREPARED THEREFROM
Abstract
The present invention relates to a method for preparing a super
absorbent polymer. The method for preparing a super absorbent
polymer according to the present invention can provide a super
absorbent resin exhibiting fast absorption rate and high saline
flow conductivity while having excellent absorption properties such
as a centrifuge retention capacity and an absorbency under
pressure, by using the polycarboxylic acid-based copolymer under
pulverization of the hydrous gel phase polymer.
Inventors: |
Lee; Yong Hun; (Daejeon,
KR) ; Ahn; Tae Bin; (Daejeon, KR) ; Han; Chang
Sun; (Daejeon, KR) ; Seo; Sung Jong; (Daejeon,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG Chem, Ltd. |
Seoul |
|
KR |
|
|
Assignee: |
LG Chem, Ltd.
Seoul
KR
|
Family ID: |
56193025 |
Appl. No.: |
15/302845 |
Filed: |
November 9, 2015 |
PCT Filed: |
November 9, 2015 |
PCT NO: |
PCT/KR2015/012000 |
371 Date: |
October 7, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 265/02 20130101;
C08F 265/04 20130101; A61L 15/60 20130101; C08F 220/06 20130101;
C08F 2/48 20130101; C08F 220/10 20130101; C08F 6/008 20130101; C08F
2/10 20130101; C08J 3/245 20130101; C08F 290/062 20130101; C08J
3/075 20130101; C08L 33/02 20130101; C08F 220/286 20200201; C08F
220/06 20130101; C08F 220/06 20130101; C08F 220/286 20200201; C08F
222/385 20130101; C08F 220/06 20130101; C08F 222/385 20130101; C08F
220/06 20130101; C08F 220/06 20130101; C08F 285/00 20130101; C08J
2333/02 20130101; C08J 3/24 20130101; C08F 285/00 20130101; C08F
290/062 20130101; C08J 3/12 20130101; A61L 15/24 20130101; C08F
265/02 20130101; C08F 265/02 20130101; C08J 2351/00 20130101; C08F
6/008 20130101; C08F 285/00 20130101; C08J 2433/10 20130101; C08F
20/10 20130101; C08F 222/385 20130101; C08F 222/385 20130101 |
International
Class: |
C08J 3/24 20060101
C08J003/24; A61L 15/24 20060101 A61L015/24; A61L 15/60 20060101
A61L015/60; C08F 265/04 20060101 C08F265/04; C08J 3/12 20060101
C08J003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2014 |
KR |
10-2014-0167735 |
Nov 6, 2015 |
KR |
10-2015-0155892 |
Claims
1. A method for preparing a super absorbent polymer comprising the
steps of: 1) carrying out thermal polymerization or
photo-polymerization of a monomer composition including a
water-soluble ethylene-based unsaturated monomer, a polymerization
initiator and a polycarboxylic acid-based copolymer having a
repeating unit represented by the following Chemical Formulas 1-a
and 1-b to prepare a hydrous gel phase polymer; 2) drying the
hydrous gel phase polymer; 3) pulverizing the dried polymer; and 4)
surface-crosslinking the pulverized polymer. ##STR00002## in
Chemical Formulas 1-a and 1-b, R.sup.1, R.sup.2 and R.sup.3 are
each independently hydrogen, or an alkyl group having 1 to 6 carbon
atoms, RO is an oxyalkylene group having 2 to 4 carbon atoms,
M.sup.1 is hydrogen, or a monovalent metal or non-metal ion, X is
--COO--, or an alkyloxy group having 1 to 5 carbon atoms, or an
alkyldioxy group having 1 to 5 carbon atoms, m is an integer of 1
to 100, n is an integer of 1 to 1000, and p is an integer of 1 to
150, provided that when p is 2 or more, two or more repeated --RO--
may be the same or different from each other.
2. The method for preparing a super absorbent polymer according to
claim 1, wherein the polycarboxylic acid-based copolymer in the
step 1 is mixed in an amount of 0.001 to 5 parts by weight based on
100 parts by weight of the water-soluble ethylene-based unsaturated
monomer.
3. The method for preparing a super absorbent polymer according to
claim 1, wherein the polycarboxylic acid-based copolymer has a
weight average molecular weight of 500 to 1,000,000.
4. The method for preparing a super absorbent polymer according to
claim 1, wherein the drying of the step 2 is carried out at a
temperature of 120.degree. C. to 250.degree. C.
5. The method for preparing a super absorbent polymer according to
claim 1, further comprising a step of pulverizing the hydrous gel
phase polymer into a particle diameter of 1 mm to 10 mm, before the
drying step of the hydrous gel phase polymer.
6. The method for preparing a super absorbent polymer according to
claim 1, wherein the pulverization of the dried polymer is carried
out so that the particle diameter of the pulverized polymer becomes
150 .mu.m to 850 .mu.m.
7. The method for preparing a super absorbent polymer according to
claim 1, wherein the surface crosslinking is carried out at a
temperature of 100 to 250.degree. C.
8. The method for preparing a super absorbent polymer according to
claim 1, wherein the surface crosslinking is carried out with one
or more crosslinking agents selected from the group consisting of
ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl
ether, glycerol polyglycidyl ether, propylene glycol diglycidyl
ether, polypropylene glycol diglycidyl ether, ethylene carbonate,
ethylene glycol, diethylene glycol, propylene glycol, triethylene
glycol, tetraethylene glycol, propanediol, dipropylene glycol,
polypropylene glycol, glycerin, polyglycerin, butanediol,
heptanediol, hexanediol, trimethylolpropane, pentaerythritol,
sorbitol, calcium hydroxide, magnesium hydroxide, aluminum
hydroxide, iron hydroxide, calcium chloride, magnesium chloride,
aluminum chloride, and iron chloride.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit of priority based on
Korean Patent Application No. 10-2014-0167735 filed on Nov. 27,
2014 and Korean Patent Application No. 10-2015-0155892 filed on
Nov. 6, 2015 with the Korean Intellectual Property Office, the
disclosures of which are incorporated herein by reference in their
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method for preparing a
super absorbent polymer which has fast absorption rate and high
saline flow conductivity while having excellent absorption
properties such as a centrifuge retention capacity and an
absorbency under pressure.
BACKGROUND OF ART
[0003] Super absorbent polymer (SAP) is a synthetic polymer
material capable of absorbing moisture from about 500 to about
1,000 times its own weight, and it has been also called a super
absorbency material (SAM), an absorbent gel material (AGM) and so
on. Such super absorbent polymers started to be practically applied
in sanitary products, and now they are widely used for preparation
of various products, for example, hygiene products such as
disposable diapers for children, water retaining soil products for
gardening, water stop materials for the civil engineering and
construction, sheets for raising seedling, fresh-keeping agents for
food distribution fields, or the like.
[0004] As a method for preparing such a super absorbent polymer, an
inverse suspension polymerization method, an aqueous solution
polymerization method or the like are known. Among them, the
preparation of super absorbent polymers via inverse suspension
polymerization is disclosed in Japanese Patent Publication Nos. Sho
56-161408, Sho 57-158209, Sho 57-198714, and so on. Furthermore,
for the preparation of super absorbent polymers via aqueous
solution polymerization, a thermal polymerization method of
polymerizing a hydrous gel phase polymer while breaking and cooling
the same in a kneader equipped with a plurality of spindles, and a
photo-polymerization method of exposing a high-concentrated aqueous
solution to UV rays or the like on a belt so as to carry out the
polymerization and drying at the same time are known.
[0005] On the other hand, the absorption rate, one of important
physical properties of super absorbent polymers is associated with
the surface dryness of the product in contact with a skin, such as
disposable diapers. In general, these absorption rates can be
improved in a manner of widening a surface area of the super
absorbent polymer.
[0006] As an example, a method of forming a porous structure on the
particle surface of the super absorbent polymer by using a blowing
agent has been applied. However, general blowing agents have a
disadvantage that a sufficient amount of the porous structure
cannot be formed arid thus the absorption rate is not highly
increased.
[0007] As another example, there is a method for increasing a
surface area of the super absorbent polymer by reassembling fine
particles obtained during preparation of the super absorbent
polymer to form a porous particle with irregular shape. However,
although the absorption rate of the super absorbent polymer can be
improved through these methods, there is a limit that a centrifuge
retention capacity (CRC) and an absorbency under pressure (AUP) of
the polymer are relatively decreased. In this way, because physical
properties such as an absorption rate, a centrifuge retention
capacity, an absorbency under pressure of the super absorbent
polymer have a trade-off relation, there is an urgent need for the
preparation method capable of improving these properties
simultaneously.
DETAILED DESCRIPTION OF THE INVENTION
Technical Problem
[0008] For resolving the aforesaid problems of the prior arts, it
is an object of the present invention to provide a method for
preparing a super absorbent polymer that has fast absorption rate
and high permeability at the same time.
Technical Solution
[0009] To achieve the above object, the present invention provides
a method for preparing a super absorbent polymer comprising the
steps of:
[0010] 1) carrying out thermal polymerization or
photo-polymerization of a monomer composition comprising a
water-soluble ethylene-based unsaturated monomer, a polymerization
initiator and a polycarboxylic acid-based copolymer having a
repeating unit represented by the following Chemical Formulas 1-a
and 1-b to prepare a hydrous gel phase polymer;
[0011] 2) drying the hydrous gel phase polymer;
[0012] 3) pulverizing the dried polymer; and
[0013] 4) surface-crosslinking the pulverized polymer:
##STR00001##
[0014] in Chemical Formulas 1-a and 1-b,
[0015] R.sup.1, R.sup.2 and R.sup.3 are each independently
hydrogen, or an alkyl group having 1 to 6 carbon atoms,
[0016] RO is an oxyalkylene group having 2 to 4 carbon atoms,
[0017] M.sup.1 is hydrogen, or a monovalent metal or non-metal
on,
[0018] X is --COO--, or an alkyloxy group having 1 to 5 carbon
atoms or an alkyldioxy group having 1 to 5 carbon atoms,
[0019] m is an integer of 1 to 100,
[0020] n is an integer of 1 to 1000, and
[0021] p is an integer of 1 to 150, provided that when p is 2 or
more, two or more repeated --RO-- may be the same or different from
each other.
[0022] For the super absorbent polymer, a centrifuge retention
capacity (CRC), an absorbency under pressure (AUP) and a saline
flow conductivity (SFC) are evaluated as important physical
properties, and especially, articles that super absorbent polymers
are used, for example, disposable diapers and the like are thinned.
Thus, having fast absorption rate and high saline flow conductivity
at the same time is considered important. In order to increase the
absorption rate, conventionally, a method for creating fine pores
in a base polymer by addition of a chemical blowing agent that
generates a gas when polymerizing super absorbent polymers, or a
method for providing a porosity by applying addition of a physical
force to the prepared hydrous gel phase polymer after the
polymerization have been used. However, there are problems that it
is difficult to significantly improve the absorption rate by using
the chemical blowing agent, and the absorption properties are
lowered by a method of simply applying a physical force to the
hydrogel. In this way, because physical properties such as an
absorption rate, a centrifuge retention capacity, an absorbency
under pressure and a saline flow conductivity of the super
absorbent polymer have a trade-off relation, there is an urgent
need for the preparation method capable of improving these
properties simultaneously.
[0023] Thus, in the present invention, by using the polycarboxylic
acid-based copolymer under polymerization of the hydrous gel phase
polymer, the polycarboxylic acid-based copolymer allows to reduce
the internal crosslinking reaction rate, thereby providing a
hydrous gel phase polymer which has uniform network structure and
less water-soluble component. This also makes it possible to obtain
fine particles which make a uniform pulverization and has a wide
surface area when pulverizing the hydrous gel phase polymer.
[0024] The present invention will now be described in detail step
by step.
[0025] Step of Preparing a Hydrous Gel Phase Polymer (Step 1)
[0026] First, the method for preparing the super absorbent polymer
comprises a step of carrying out thermal polymerization or
photo-polymerization of a monomer composition including a
water-soluble ethylene-based unsaturated monomer, a polymerization
initiator and a polycarboxylic acid-based copolymer to prepare a
hydrous gel phase polymer.
[0027] Particularly, in the present invention, the polycarboxylic
acid-based copolymer as defined above is used together. As an
example, as the polycarboxylic acid-based copolymer, random
copolymers derived from hydrophilic monomers such as alkoxy
polyalkylene glycol mono(meth)acrylic acid ester-based monomer (as
a representative example, methoxy polyethylene glycol
monomethacrylate (MPEGMAA), etc.) and (meth)acrylic acid
ester-based monomer (as a representative example, (meth)acrylic
acid, etc.) can used, and these may be more advantageous for the
expression of the effects described above.
[0028] Also, in order to better express the effects resulting from
the addition of the polycarboxylic acid-based copolymer, the
polycarboxylic acid-based copolymer has preferably a weight average
molecular weight of 500 to 1,000,000.
[0029] Moreover, the content of the carboxylic acid-based copolymer
may be appropriately adjusted depending on the kind and reaction
conditions of the copolymer, and preferably it can be adjusted in
the range of 0.001 to 5 parts by weight based on 100 parts by
weight of the water-soluble ethylene-based unsaturated monomer.
When the content of the polycarboxylic acid-based copolymer is
excessively low, the above-described effects of the present
invention may not be sufficiently exhibited. In contrast, when the
content of the polycarboxylic acid-based copolymer is used
excessively, functions inherent in the super absorbent polymer are
lowered, and the absorption properties are reduced or it may result
in a reduction in the surface tension or in the powder flow
property, which is not preferable. More preferably, the content of
the polycarboxylic acid-based copolymer is 0.01 parts by weight or
more, 0.1 parts by weight or more, 0.2 parts by weight or more, or
0.3 parts by weight or more, and 4 parts by weight or less, 3 parts
by weight or less, 2 parts by weight or less, or 1 part by weight
or less, based on based on 100 parts by weight of the water-soluble
ethylene-based unsaturated monomer.
[0030] The water-soluble ethylene-based unsaturated monomer
included in the monomer composition may be any monomer that is
generally used in the preparation of the super absorbent polymer.
In a non-limiting example, the water-soluble ethylene-based
unsaturated monomer may be a compound represented by the following
Chemical Formula 3:
R.sub.4--COOM.sup.2 [Chemical Formula 3]
[0031] in Chemical Formula 3,
[0032] R.sub.4 is a C.sub.2-C.sub.5 alkyl group comprising an
unsaturated bond, and
[0033] M.sup.2 is a hydrogen atom, a monovalent or divalent metal,
an ammonium group, or an organic amine salt.
[0034] Preferably, the above-mentioned monomers may be one or more
selected from the group consisting of acrylic acid, methacrylic
acid, and monovalent or divalent metal salts of these acids,
ammonium salts and organic amine salts. Thus, when using acrylic
acid or a salt thereof as the water-soluble ethylene-based
unsaturated monomer as described above, it is advantageous because
the super absorbent polymer having improved water absorption
properties can be obtained. In addition, as the monomers, maleic
anhydride, fumalic acid, crotonic acid, itaconic acid,
2-acryloylethane sulfonic acid, 2-methacryloylethane sulfonic acid,
2-(meth)acryloylpropane sulfonic acid, or
2-(meth)acrylamide-2-methyl propane sulfonic acid,
(meth)acrylamide, N-substituted (meth)acrylate,
2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate,
methoxypolyethyleneglycol (meth)acrylate,
polyethyleneglycol(meth)acrylate,
(N,N)-dimethylaminoethyl(meth)acrylate,
(N,N)-dimethylaminopropyl(meth)acrylate, and the like may be
used.
[0035] Here, the water-soluble ethylene-based unsaturated monomer
may have an acidic group in which at least a part of the acidic
group is neutralized. Preferably, the monomers that are used herein
may include those partially neutralized with an alkaline substance
such as sodium hydroxide, potassium hydroxide, or ammonium
hydroxide.
[0036] In this case, the degree of neutralization of the monomer
may be 40 to 95 mol %, or 40 to 80 mol %, or 45 to 75 mol %. The
range of the degree of neutralization may vary depending on the
final physical properties. However, if the degree of neutralization
is too high, the neutralized monomer may be precipitated and thus
it may be difficult to perform polymerization smoothly. In
contrast, if the degree of neutralization is too low, the
absorptive capacity of the polymer is greatly reduced and also it
may exhibit elastic rubber-like properties which are
difficult-to-handle.
[0037] Further, the concentration of the water-soluble ethylene
based unsaturated monomer in the monomer composition may be
appropriately controlled in consideration of a polymerization time,
a reaction condition and the like, and it may be preferably 20 to
90% by weights or 40 to 65% by weights. Such concentration range
may be advantageous to control the pulverizing efficiency during
pulverization of the polymer which will be described later, while
eliminating the necessity of removing non-reacted monomers after
polymerization using a gel effect phenomenon that appears in the
polymerization reaction of high-concentration aqueous solutions.
However, if the concentration of the monomer is too low, the yield
of the super absorbent polymer may be decreased. In contrast, if
the concentration of the monomer is too high, there may be a
process problem that a part of the monomers may be precipitated or
pulverization efficiency may be lowered upon pulverization of the
polymerized hydrous gel phase polymer, and physical properties of
the super absorbent polymer may be degraded.
[0038] Meanwhile, the monomer composition may include a
polymerization initiator that is generally used in the preparation
of the super absorbent polymer. In a non-limiting example, the
polymerization initiator that can be used herein includes a thermal
polymerization initiator, a photo-polymerization initiator or the
like, depending on the polymerization method. However, even in the
case of using the photo-polymerization method, because a certain
amount of heat is generated by the ultraviolet irradiation or the
like and a certain degree of heat is generated according to the
progress of the polymerization reaction, i.e., exothermic reaction,
a thermal polymerization initiator may be additionally included
[0039] Here, the photo-polymerization initiator, for example, may
include one or more compounds selected from the group consisting of
a benzoin ether, a dialkyl acetophenone, a hydroxyl alkylketone, a
phenyl glyoxylate, a benzyl dimethyl ketal, an acyl phosphine, and
.alpha.-aminoketone. Among them, specific examples of the acyl
phosphine may include normal lucirin TPO, namely,
2,4,6-trimethyl-benzoyl-trimethyl phosphine oxide. More various
photo-polymerization initiators are disclosed in "UV Coatings:
Basics, Recent Developments and New Application (Elsevier, 2007),
p115," written by Reinhold Schwalm, which is incorporated herein by
reference.
[0040] And, as the thermal polymerization initiator, one or more
compounds selected from the group consisting of a persulfate-based
initiator, an azo-based initiator, hydrogen peroxide, and ascorbic
acid may be used. Specific examples of the persulfate-based
initiator may include sodium persulfate (Na.sub.25.sub.2O.sub.8),
potassium persulfate (K.sub.2S.sub.2O.sub.8), ammonium persulfate
((NH.sub.4).sub.2S.sub.2O.sub.8), and the like. Also, examples of
the azo-based initiator may include
2,2-azobis(2-amidinopropane)dihydrochloride,
2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride,
2-(carbamoylazo)isobutylonitrile,
2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,
4,4-azobis-(4-cyanovaleric acid) and the like. More various thermal
polymerization initiators are disclosed in "Principle of
Polymerization (Wiley, 1981), p203" written by Odian, which is
incorporated herein by reference.
[0041] These polymerization initiators may be included in the
concentration of about 0.001% to 1% by weight based on the monomer
composition. That is, when the concentration of the polymerization
initiator is too low, it is not preferable because the
polymerization rate may become slow and residual monomer in the
final product can be extracted in a large amount. In contrast, when
the concentration of the photo-polymerization initiator is too
high, it is not preferable because physical properties of the
polymer may be deteriorated, for example, the polymer chain forming
a network is shortened, the content of water-soluble component is
increased and the absorbency under pressure is lowered.
[0042] Meanwhile, the monomer composition may further include a
crosslinking agent ("internal crosslinking agent") in order to
improve physical properties of the polymer by the polymerization of
the water-soluble ethylene-based unsaturated monomer. The
crosslinking agent is for the internal crosslinking of the hydrous
gel phase polymer and it can be used separately from a crosslinking
agent for crosslinking the surface of the hydrous gel phase polymer
("surface crosslinking agent").
[0043] As the internal crosslinking agent, any compound can be used
as long as it allows the formation of crosslinks during
polymerization of the water-soluble ethylene-based unsaturated
monomer.
[0044] In an non -limiting example of the internal crosslinking
agents, polyfunctional crosslinking agents such as
N,N'-methylenebisacrylamide, trimethylolpropane, tri(meth)acrylate,
ethylene glycol di(meth)acrylate, polyethylene
glycol(meth)acrylate, polypropylene glycol di(meth)acrylate,
polypropylene glycol(meth)acrylate, butanediol di(meth)acrylate,
butylene glycol di(meth)acrylate, diethylene glycol
di(meth)acrylate, hexanedial di(meth)acrylate, triethylene glycol
di(meth)acrylate, tripropylene glycol di(meth)acrylate,
tetraethylene glycol di(meth)acrylate, dipentaerythritol
pentaacrylate, glycerin tri(meth)acrylate, pentaerythritol
tetraacrylate, triallylamine, ethylene glycol diglycidyl ether,
propylene glycol, glycerin, or ethylene carbonate can be used
alone, or two or more thereof can be used in combination, but are
not limited thereto.
[0045] Such internal crosslinking agent may be included in the
concentration of about 0.001% to 1% by weight based on the monomer
composition. In other words, if the concentration of the internal
crosslinking agent is too low, it is not preferable because the
absorption rate of the polymer is lowered and the gel strength can
be reduced. In contrast, if the concentration of the internal
crosslinking agent is too high, the absorptive capacity is lowered
and thus it may be not preferable as an absorber.
[0046] In addition, the monomer composition may further include
additives such as a thickener, a plasticizer, a preservation
stabilizer, an antioxidant, and so on, as needed.
[0047] Further, the monomer composition may be prepared in the form
of a solution in which the raw materials such as the
above-mentioned monomer, the polymerization initiator or the
internal crosslinking agent are dissolved in a solvent.
[0048] In this case, as the solvent usable herein, any solvent can
be used without limitation in the construction as long as it allows
to dissolve the above-described raw materials. For example, as the
solvent, water, ethanol, ethyleneglycol, diethyleneglycol,
triethyleneglycol, 1,4-butanediol, propyleneglycol, ethyleneglycol
monobutylether, propyleneglycol monomethylether, propyleneglycol
monomethylether acetate, methylethylketone, acetone,
methylamylketone, cyclohexanone, cyclopentanone, diethyleneglycol
monomethylether, diethyleneglycol ethylether, toluene, xylene,
butylolactone, carbitol, methylcellosolve acetate, N,N-dimethyl
acetamide, or mixtures thereof may be used.
[0049] Further, the formation of the hydrous gel phase polymer
through the polymerization of the monomer composition can be
carried out by a conventional polymerization method, and the
process thereof is not particularly limited. In a non-limiting
example, the polymerization method is largely classified into a
thermal polymerization and a photo-polymerization depending on the
type of the polymerization energy source. The thermal
polymerization may be carried out in a reactor like a kneader
equipped with agitating spindles, and the photo-polymerization may
be carried out in a reactor equipped with a movable conveyor
belt.
[0050] As an example, the thermal polymerization can be carried out
by injecting the monomer composition into a reactor such as a
kneader equipped with the agitating spindles and then supplying hot
air to the reactor or heating the reactor, thereby obtaining a
hydrous gel phase polymer. The hydrous gel phase polymer discharged
from the outlet of the reactor may be obtained as a particle having
a size of centimeters or millimeters, depending on the type of the
agitating spindles equipped in the reactor. Specifically, the
hydrous gel phase polymer may be obtained into various shapes
depending on the monomer concentration, the injection rate or the
like of the monomer composition injected thereto, and the hydrous
gel phase polymer having a (weight average) particle diameter of 2
mm to 50 mm can be generally obtained.
[0051] Further, as another example, when the photo-polymerization
of the monomer composition is carried out in a reactor equipped
with a movable conveyor belt, the hydrous gel phase polymer in the
form of a sheet can be obtained. In this case, the thickness of the
sheet may vary depending on the concentration and the injection
rate of the monomer composition injected thereto. However,
typically it is preferable to adjust to a thickness of 0.5 cm to 5
cm, in order to ensure the production speed or the like while
allowing a uniform polymerization of the entire sheet.
[0052] The hydrous gel phase polymer obtained by the
above-mentioned methods may have typically a moisture content of
about 40% to about 80% by weight. As used here, the term "moisture
content" refers to the content of moisture occupied based on total
weight of the hydrous gel phase polymer, and it may be a value
calculated by subtracting the weight of the dried polymer from the
weight of the hydrous gel phase polymer. Specifically, it may be
defined by the value calculated by measuring the weight loss
according to evaporation of water in the polymer in the process of
raising the temperature of the polymer and drying it through
infrared heating. In this case, the drying condition is that the
temperature is raised from the room temperature to about 180.sup.00
and then maintained at 180.degree. C., and thereby the total drying
time can be set to 20 minutes including the temperature raising
step for 5 minutes
[0053] Step of Drying the Hydrous Gel Phase Polymer (Step 2)
[0054] Meanwhile, the method for preparing a super absorbent
polymer comprises a step of drying the hydrous gel phase polymer
formed through the aforementioned step.
[0055] Here, if necessary, to increase the efficiency of the drying
step, a step of pulverizing (coarsely pulverizing) the hydrous gel
phase polymer before the drying step can be further performed.
[0056] In an non-limiting example, a pulverizing device usable in
the coarse pulverization may include a vertical pulverizer, a turbo
cutter, a turbo grinder, a rotary cutter mill, a cutter mill, a
disc mill, a shred crusher, a crusher, a chopper, a disc cutter and
the like.
[0057] In this case, the coarse pulverization may be carried out so
that the particle diameter of the hydrous gel phase polymer becomes
1 mm to 10 mm. In other words, in order to increase the drying
efficiency, the hydrous gel phase polymer is preferably pulverized
into a particle diameter of 10 mm or less. However, upon excessive
pulverization, the aggregation phenomenon between particles may
occur and thus, the hydrous gel phase polymer is preferably
pulverized into a particle diameter of 1 mm or more.
[0058] Further, when the coarsely pulverizing step is carried out
before the drying step of the hydrous gel phase polymer as
described above, the hydrous gel phase polymer is in a state where
moisture content is high and thus, a phenomenon where the polymer
sticks to the surface of the pulverizer may occur. In order to
minimize this phenomenon, in the coarsely pulverizing step, fine
particle aggregation preventing agents such as steam, water,
surfactant, clay or silica; thermal polymerization initiators such
as persulfate-based initiators, azo-based initiators, hydrogen
peroxide and ascorbic acid, epoxy-based crosslinking agents, diol
crosslinking agents, crosslinking agents containing
multi-functional groups of di-, tri- or higher functional groups,
crosslinking agents such as a compound with mono-functional group
including hydroxy group may be used as needed.
[0059] Meanwhile, the drying of the hydrous gel phase polymer
immediately after the coarse pulverization or polymerization as
described above may be carried out at a temperature of 120.degree.
C. to 250.degree. C., or 150.degree. C. to 200.degree. C., or
160.degree. C. to 180.degree. C. (In this case, the above
temperature can be defined as the temperature of a heating medium
provided for drying or the internal temperature of drying reactors
containing a heating medium and a polymer in the drying step). That
is, if the drying temperature is low and the drying time is
prolonged, the physical properties of the final polymer may be
decreased. Thus, in order to prevent these problems, the drying
temperature is preferably 120.degree. C. or higher. Further, if the
drying temperature is higher than necessary, only the surface of
the hydrous gel phase polymer is dried, and thus a generation
amount of fine powders may be increased during the pulverizing step
to be described later and the physical properties of the final
polymer may be deteriorated. Thus, in order to prevent these
problems, the drying temperature is preferably 250.degree. C. or
less.
[0060] At this time, the drying time for the drying step is not
particularly limited, but the drying time may be adjusted in the
range of 20 minutes to 90 minutes at the above-mentioned drying
temperature, in consideration of the process efficiency or the
like, but it is not particularly limited thereto.
[0061] Further, in the drying step, any drying method may be used
without limitation in the construction as long as it is generally
known to be usable for the drying process of the hydrous gel phase
polymer. Specifically, the drying step may be carried out by a
method such as hot air supply, infrared irradiation, microwave
irradiation or ultraviolet irradiation.
[0062] The polymer dried by the above-described method can exhibit
a moisture content of about 0.1% to 10% by weight. In other words,
if the moisture content of the polymer is less than 0.1% by weight,
it may cause excessively drying and thus production costs may
increase and the crosslinked polymer may degrade, which is not
advantageous. In addition, if the moisture content is greater than
10% by weight, it is not preferable because a defect may occur in a
subsequent step.
[0063] Step of Pulverizing the Dried Polymer (Step 3)
[0064] Meanwhile, the method for preparing a super absorbent
polymer comprises a step of pulverizing the polymer dried through
the aforementioned step.
[0065] The pulverizing step is a step for optimizing the surface
area of the dried polymer, and it can be carried out so that the
particle diameter of the pulverized polymer becomes 150 .mu.m to
850 .mu.m. Examples of a pulverizing device that can be used to
pulverize into the above particle diameter may include a pin mill,
a hammer mill, a screw mill, a roll mill, a disc mill, a jog mill
or the like.
[0066] In addition, in order to control the physical properties of
the super absorbent polymer powder finally manufactured, a step of
selectively classifying particles having a particle diameter of 150
.mu.m to 850 .mu.m from the polymer powders obtained through the
pulverizing step can be further carried out.
[0067] Step of Surface-Crosslinking the Pulverized Polymer (Step
4)
[0068] Meanwhile, the method for preparing a super absorbent
polymer comprises a step of surface-crosslinking the polymer
pulverized through the aforementioned steps.
[0069] The surface crosslinking is a step for increasing the
crosslinking density near the surface of the polymer particles, and
it can be carried out by a method of mixing a solution containing a
crosslinking agent (surface crosslinking agent) with the pulverized
polymer to perform crosslinking reaction.
[0070] Here, the kind of the crosslinking agent (surface
crosslinking agent) contained in the surface cross-linking solution
is not particularly limited. In a non-limiting example, the surface
crosslinking agent may be one or more compounds selected from the
group consisting of ethylene glycol diglycidyl ether, polyethylene
glycol diglycidyl ether, glycerol polyglycidyl ether, propylene
glycol diglycidyl ether, polypropylene glycol diglycidyl ether,
ethylene carbonate, ethylene glycol, diethylene glycol, propylene
glycol, triethylene glycol, tetraethylene glycol, propanediol,
dipropylene glycol, polypropylene glycol, glycerin, polyglycerin,
butanediol, heptanediol, hexanediol, trimethylolpropane,
pentaerythritol, sorbitol, calcium hydroxide, magnesium hydroxide,
aluminum hydroxide, iron hydroxide, calcium chloride, magnesium
chloride, aluminum chloride, and iron chloride.
[0071] At this time, the amount of the surface crosslinking agent
may be appropriately adjusted depending on the kind of the
crosslinking agent or the reaction conditions, and preferably can
be adjusted in the range of 0.001 to 5 parts by weight based on 100
parts by weight of the pulverized polymer. If the amount of the
surface crosslinking agent is too low, the surface crosslink is not
properly introduced and the physical properties of the final
polymer can be reduced. In contrast, if the surface crosslinking
agent is used in an excessively large amount, the absorptive
capacity of the polymer may be lowered due to excessive surface
crosslinking reaction, which is not desirable.
[0072] In the meantime, in order to carry out the surface
crosslinking step, a method of adding the surface crosslinking
solution and the pulverized polymer to a reaction tank and then
mixing them, a method of spraying the surface crosslinking solution
onto the pulverized polymer, a method of continuously supplying the
pulverized polymer and the surface crosslinking solution to a mixer
being continuously operated and then mixing them, and the like can
be used.
[0073] Furthermore, when the surface crosslinking solution is
added, water may be further added. Thus, by adding water together,
more uniform dispersion of the crosslinking agent can be induced,
the aggregation phenomenon of the polymer powder can be prevented,
and the penetration depth of the surface crosslinking agent for the
polymer powder can be more optimized. In consideration of these
objects and advantages, the amount of water to be added can be
adjusted in the range of 0.5 to 10 parts by weight relative to 100
parts by weight of the pulverized polymer.
[0074] Furthermore, the surface crosslinking step may be carried
out at a temperature of 100.degree. C. to 250.degree. C., and it
can be continuously made after the drying and pulverizing steps
being conducted at a relatively high temperature. At this time, the
surface crosslinking reaction can be carried out for 1 to 120
minutes, or 1 to 100 minutes, or 10 to 60 minutes. That is, in
order to prevent the polymer particles from being damaged due to
excessive surface reaction to lead to deterioration in the physical
properties, while inducing surface crosslinking reaction to the
minimum, the surface crosslinking can be carried out under the
above-described reaction conditions.
[0075] By using these methods, a super absorbent polymer having
less generation amount of coarse particles and fine particles,
exhibiting fast absorption rate and high saline flow conductivity
while having absorption properties such as a centrifuge retention
capacity and an absorbency under pressure can be prepared.
Advantageous Effects
[0076] The method for preparing a super absorbent polymer according
to the present invention can provide a super absorbent polymer
exhibiting fast absorption rate and high saline flow conductivity
while having excellent absorption properties such as a centrifuge
retention capacity and an absorbency under pressure, by using the
polycarboxylic acid-based copolymer under pulverization of the
hydrous gel phase polymer.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0077] Hereinafter, the preferred Examples are provided for better
understanding of the invention. However, these Examples are given
for illustrative purposes only and not intended to limit the scope
of the present invention.
Preparation Example 1
[0078] 400 parts by weight of ion exchanged water was added to a 3
L four-neck flask reactor equipped with a stirrer, a thermometer, a
nitrogen feeder and a circulating condenser, nitrogen was fed into
the reactor while stirring, and the reactor was heated up to
75.degree. C. under the nitrogen atmosphere.
[0079] Subsequently, 2 parts by weight of ammonium persulfate was
added to the reactor and the resulting solution was completely
dissolved. Then, an aqueous monomer solution prepared by mixing 600
parts by weight of methoxypolyethylene glycol monomethacrylate
(average addition mole number of ethylene oxide (EO): about 50
moles), 96.6 parts by weight of methacrylic acid and 190 parts by
weight of water, a mixed solution of 5 parts by weight of
3-mercaptopropionic acid and 5 parts by weight of water, and 150
parts by weight of a 3 wt % aqueous ammonium persulfate solution
were continuously added to the reactor at a uniform speed for 4
hours. After completion of the addition, 5 parts by weight of a 3
wt % aqueous ammonium persulfate solution was added again thereto
at a time.
[0080] Then, after raising the internal temperature of the reactor
to 85.degree. C., the reaction continued for 1 hour while
maintaining the temperature at 85.degree. C. to complete
polymerization reaction.
[0081] The weight average molecular weight of the polycarboxylic
acid-based copolymer thus prepared has a weight average molecular
weight of 40,000, as measured by gel permeation chromatography
(GPO).
Preparation Example 2
[0082] The polycarboxylic acid-based copolymer (weight average
molecular weight: 40,000) was prepared in the same manner in
Preparation Example 1, with the exception that it was neutralized
with a 30 wt % aqueous triethanolamine solution for about 1 hours,
after completion of the polymerization reaction as in Preparation
Example 1.
Preparation Example 3
[0083] The polycarboxylic acid-based copolymer (weight average
molecular weight: 40,000) was prepared in the same manner in
Preparation Example 2, with the exception that it was neutralized
with an aqueous sodium hydroxide solution instead of an aqueous
triethanolamine solution.
Preparation Example 4
[0084] 300 parts by weight of ion exchanged water was added to a 3L
four-neck flask reactor equipped with a stirrer, a thermometer, a
nitrogen feeder and a circulating condenser, nitrogen was fed into
the reactor while stirring, and the reactor was heated up to
75.degree. C. under the nitrogen atmosphere.
[0085] Subsequently, 2 parts by weight of ammonium persulfate was
added to the reactor and the resulting solution was completely
dissolved. Then, an aqueous monomer solution prepared by mixing 300
parts by weight of methoxypolyethylene glycol monomethacrylate
(average addition mole number of ethylene oxide(EO): about 50
moles), 49.8 parts by weight of methacrylic acid and 50 parts by
weight of water, a mixed solution of 5 parts by weight of
3-mercaptopropionic acid and 30 parts by weight of water, and 80
parts by weight of a 3 wt % aqueous ammonium persulfate solution
were continuously added to the reactor at a uniform speed for 4
hours. After completion of the addition, 5 parts by weight of a 3
wt % aqueous ammonium persulfate solution was added again thereto
at a time.
[0086] Then, after raising the internal temperature of the reactor
to 85.degree. C., the reaction continued for 1 hour while
maintaining the temperature at 85.degree. C. to complete
polymerization reaction.
[0087] The polycarboxylic acid-based copolymer thus prepared showed
that it had a weight average molecular weight of 45,000, as
measured by gel permeation chromatography (GPC).
Preparation Example 5
[0088] The polycarboxylic acid-based copolymer (weight average
molecular weight: 45,000) was prepared in the same manner in
Preparation Example 4, with the exception that it was neutralized
with a 30 wt % aqueous triethanolamine solution for about 1 hours,
after completion of the polymerization reaction as in Preparation
Example 4.
Preparation Example 6
[0089] The polycarboxylic acid-based copolymer (weight average
molecular weight: 45,000) was prepared in the same manner in
Preparation Example 5, with the exception that it was neutralized
with an aqueous sodium hydroxide solution instead of an aqueous
triethanolamine solution.
Example 1
[0090] About 5 g of N,N'-methylene bisacrylamide as an internal
crosslinking agent and 2 g of the polycarboxylic acid-based
copolymer according to Preparation Example 1 were mixed with 500 g
of acrylic acid to which about 971.4 g of 20% aqueous sodium
hydroxide solution was added to prepare a monomer composition
(neutralization degree of the acrylic acid-based monomer: 70 mol
%).
[0091] The monomer composition was put in a 5L tween-arm kneader
having sigma-shaped spindles, and nitrogen gas was added for 30
minutes while maintaining the temperature at 65.degree. C., thereby
eliminating oxygen dissolved in the aqueous solution. 30.0 g of 0.2
wt % aqueous L-ascorbic acid solution, 50.5 g of aqueous sodium
persulfate solution and 30.0 g of 2.0 wt % aqueous hydrogen
peroxide solution were added thereto while stirring. Polymerization
was initiated after 5 seconds, and the resulting gel was finely
divided for 3 minutes by applying a shearing force of the twin-arm
kneader. The divided hydrogel crosslinked polymer was removed from
the kneader. The resulting hydrogel crosslinked polymer was put in
a meat chopper (manufactured by SL Corporation, the discharge port
with a mesh hole diameter of 10 mm) and divided to be less than 5
mm.
[0092] The finely divided gel was spread on a stainless wire gauze
having a hole size of 600 .mu.m to a thickness of about 30 mm, and
dried in a hot air oven at 150.degree. C. for 4 hours. The dried
polymer thus obtained was pulverized by using a pulverizing device
and then size-classified through a standard mesh sieve according to
ASTM standard to obtain an absorbent polymer powder having a
particle size of 150 to 850 .mu.m.
[0093] Then, to 100 parts by weight of the polymer powder, a
surface crosslinking solution containing 0.3 g of ethylene
carbonate (surface crosslinking agent), 3 g of methanol and 3 g of
water were added and uniformly mixed, and then dried in a hot air
oven at 180.degree. C. for 30 minutes. The dried powder was
size-classified with a standard mesh sieve according to ASTM
standard to obtain a super absorbent resin having a particle size
of 150 .mu.m to 850 .mu.m.
Example 2
[0094] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that the polycarboxylic
acid-based copolymer according to Preparation Example 2 instead of
Preparation Example 1 was used.
Example 3
[0095] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that the polycarboxylic
acid-based copolymer according to Preparation Example 3 instead of
Preparation Example 1 was used.
Example 4
[0096] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that the polycarboxylic
acid-based copolymer according to Preparation Example 4 instead of
Preparation Example 1 was used.
Example 5
[0097] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that the polycarboxylic
acid-based copolymer according to Preparation Example 5 instead of
Preparation Example 1 was used.
Example 6
[0098] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that the polycarboxylic
acid-based copolymer according to Preparation Example 6 instead of
Preparation Example 1 was used.
Comparative Example 1
[0099] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that the polycarboxylic
acid-based copolymer according to Preparation Example 1 was not
added.
Comparative Example 2
[0100] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that polyethylene glycol
(PEG-200) was added in the same amount, instead of the
polycarboxylic acid-based copolymer according to Preparation
Example 1.
Comparative Example 3
[0101] The super absorbent polymer was obtained in the same manner
as in Example 1, with the exception that 1 g of sodium bicarbonate
was added instead of the polycarboxylic acid-based copolymer
according to Preparation Example 1.
Experimental Example 1
[0102] In order to evaluate the physical properties of the super
absorbent polymers prepared in Examples and Comparative Examples,
the following experiments were carried out and the results were
shown in Table 1 below.
[0103] (1) CRC (Centrifuge Retention Capacity)
[0104] The centrifuge retention capacity of the absorbent polymer
prepared in Examples and Comparative Examples was evaluated in
accordance with the method EDANA WSP 241.2. That is, the polymers W
(g) (about 0.2 g) obtained in Examples and Comparative Examples
were uniformly put in a nonwoven fabric-made bag, followed by
sealing. Then, the bag was immersed in a physiological saline
solution (0.9 wt %) at room temperature. After a lapse of 30
minutes, water was removed from the bag using a centrifugal
separator under conditions of 250 G for 3 minutes, and the weight
W2 (g) of the bag was then measured. Further, the same procedure
was carried out without using the polymer, and then the resultant
weight W1 (g) was measured. Thus, CRC (g/g) was calculated from the
respective weights thus obtained, according to the following
Mathematical Formula.
CRC (g/g)={(W2-W1)/(W-1)} [Mathematical Formula 1]
[0105] (2) Absorbency Under Pressure (AUP)
[0106] The absorbency under pressure was measured for the absorbent
polymers prepared in Examples and Comparative Examples in
accordance with the method EDANA WSP 242.3. That is, a 400 mesh
stainless steel net was installed in the cylindrical bottom of a
plastic having an internal diameter of 60 mm. The absorbent polymer
W (g) (about 0.90 g) was uniformly scattered on the steel net under
conditions of room temperature and humidity of 50%, and a piston
which can provide a load of 4.83 kPa (0.7 psi) uniformly was put
thereon. The external diameter of the piston was slightly smaller
than 60 mm, there was no gap between the cylindrical internal wall
and the piston, and the jig-jog of the cylinder was not
interrupted. At this time, the weight Wa (g) of the device was
measured.
[0107] After putting a glass filter having a diameter of 90 mm and
a thickness of 5 mm in a Petri dish having a diameter of 150 mm, a
physiological saline solution composed of 0.90 wt % of sodium
chloride was poured in the dish until the surface level became
equal to the upper surface of the glass filter. A sheet of filter
paper having a diameter of 90 mm was put thereon. The measuring
device was put on the filter paper and the solution was absorbed
under a load for about 1 hour. After 1 hour, the weight Wb (g) was
measured after lifting the measuring device up. Thus, the
absorbency under pressure (g/g) was calculated from the Wa and Wb,
according to the following Mathematical Formula.
AUP (g/g)={Wb-Wa}/W [Mathematical Formula 2]
[0108] (3) Saline Flow Conductivity (SFC)
[0109] The saline flow conductivity was measured in accordance with
the method disclosed in paragraphs [0184] to [0189] of Column 16 of
U.S. patent application publication No. 2009-0131255.
[0110] (4) Vortex
[0111] 50.0.+-.1.0 mL of 0.9% NaCl solution was added to a 100 mL
beaker. A cylindrical stirring bar (30.times.6 mm) was added
thereto, and the above solution was stirred on the stirring plate
at 600 rpm. 2.000.+-.0.010 g of water absorbent polymer particles
were added at a time to the beaker as quickly as possible. The
stopwatch was started while starting the addition. The stopwatch
was stopped when the surface of the mixture was in a "still" state.
The above state means that the surface has no whirling. At this
time, the mixture was still rotated, but the entire surface of the
particles will be rotated as one unit. The time displayed on the
stopwatch was recorded as a vortex time.
TABLE-US-00001 TABLE 1 CRC AUP SFC Vortex (g/g) (g/g) (cm.sup.3 sec
10.sup.-7/g) (sec) Example 1 30.6 24.8 53 47 Example 2 30.6 25.0 52
47 Example 3 30.5 25.0 55 48 Example 4 30.6 24.8 51 46 Example 5
30.5 24.7 50 48 Example 6 30.5 24.9 52 46 Comparative 30.5 24.5 46
60 Example 1 Comparative 30.8 24.4 44 56 Example 2 Comparative 30.2
23.9 39 48 Example 3
[0112] As shown in Table 1, it was confirmed that the super
absorbent polymers according to Examples had fast absorption rate
and high saline flow conductivity (SFC) while exhibiting a
centrifuge retention capacity and an absorbency under pressure
equivalent to or higher than those of the super absorbent polymers
according to Comparative Examples.
[0113] Meanwhile, in the case of using a hydrophilic polymer which
was commercially available as in Comparative Example 2, the
physical properties as in Examples had not been expressed, and even
in the case of using a blowing agent which generates a gas under
polymerization as in Comparative Example 3, the absorption rate and
the saline flow conductivity were not satisfied at the same time.
Accordingly, it could be confirmed that in accordance with the
preparation method of the present invention, a super absorbent
polymers having fast absorption rate and high saline flow
conductivity at the same time could be prepared.
* * * * *